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G a O�a John Ronald Reagan Blvd.,Suite 210 <br /> CO■ y 970 8 0 00.330 aGa IowayUS.com <br /> Memorandum <br /> To: Alan Overton, PE (Fort Morgan Farms, LLC) <br /> From: Suleyman Akalin, PE, PhD, CFM (Galloway, Inc.) <br /> Date: August 18, 2021 <br /> Re: Response to Technical Revision No. 1 (TR-01); Hydraulic Analysis <br /> Report Review Memo date July 19, 2021 by Division of Reclamation, <br /> Mining and Safety (GAL Project No. FMF00001.25) <br /> Introduction <br /> This memorandum is written in response to a comment made by the Division of Reclamation, <br /> Mining and Safety (DRMS) regarding the analysis presented in the April 16th, 2021 Delta <br /> Reservoir West Cell Preliminary and East Cell Conceptual Design technical memo. DRMS <br /> noted that it is unclear from the April 16th technical memo how the design would perform in a <br /> scenario where the 1-PAC event flows occur in the South Platte River(SPR) while flows equal <br /> to or less than the 4-PAC event occurs in the Cache la Poudre River (CLPR). The current <br /> memorandum seeks to address this comment while showing that a primary design objective is <br /> still achieved: the eastern cell is filled to capacity before the peak of the 1-PAC SPR event <br /> hydrograph reaches the site. <br /> Hydrologic Information Update and Model Setup <br /> For the initial submittal, stream gage information for the CLPR and SPR has already been <br /> gathered and incorporated into a 2-D HEC-RAS model as flow hydrograph boundary conditions <br /> placed long the edge of the model grid. Two new hydrographs were generated for the CLPR: <br /> a shifted 4-PAC hydrograph and an unshifted 4-PAC hydrograph. The unshifted CLPR 4-PAC <br /> hydrography is not shifted relative to the SPR hydrograph and peaks at the site significantly <br /> sooner, while the shifted CLPR 4-PAC hydrograph is shifted to coincide with the SPR 1-PAC <br /> hydrograph peak. Both the shifted and unshifted 4-PAC CLPR hydrographs were scaled from <br /> the magnitude of the 1-PAC peak discharge to the magnitude of the 4-PAC peak discharge. <br /> Two new HEC-RAS models were created that analyze scenarios where a 4-PAC shifted and <br /> unshifted flow hydrograph is implemented along the CLPR. <br /> Hydraulic Analysis Results and Conclusions <br /> For both hydraulic analyses,the key result of the model that was evaluated was whether <br /> or not the east cell is full or nearly full when the SPR peak flow passes the site. During the <br /> previous analysis where both rivers were flowing with 1-PAC storm events, the east cell was <br /> completely full when the SPR peak flows passed the site. This is critical for the performance of <br /> the bank protection implemented along the rim of the east cell. <br /> During the shifted scenario (Design 6), the CLPR peaks at roughly the same time as <br /> the SPR. Both storms were set to begin on April 25th at 11 am with the SPR Peak discharge <br /> occurring several days later on May 1st at midnight. From the resulting simulation for Design 6, <br /> the east cell reaches full capacity on May 151 at 1 pm, several hours before the SPR peak <br /> arrives. The source of water that fills the east cell is the overbank flow coming from the rising <br /> FMF_Tech Response Memo-20210818.docx <br /> Page 1 of 4 <br />